Grade 80 Reinforcing Bars and ACI 318-71

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Title: Grade 80 Reinforcing Bars and ACI 318-71

Author(s): Paul F. Rice and David P. Gustafson

Publication: Journal Proceedings

Volume: 73

Issue: 4

Appears on pages(s): 199-206

Keywords: anchorage (structural);beams (supports);building codes;columns (supports); concrete construction;concrete slabs;construction costs;cracking (fracturing); deflection;flexural strength;high strength steels; joists;reinforced concrete: reinforcing steels.

Date: 4/1/1976

Abstract:
Reinforcement with f, = 80 ksi (5600 kgf/cm2), called Grade 80 herein, is the highest strength steel (except for prestressing tendons) permitted by the ACI Building Code. The purpose of this paper is to examine the effects of Code provisions on the use of Grade 80 steel, and to determine if savings in weight and in-place costs would result from using Grade 80 steel in some common structural elements and systems designed in accordance with the Code. Comparisons are made with Grade 60 steel. It was found that Code serviceability provisions for crack control, exterior exposure condition, limit usage of larger size Grade 80 bars. Deeper sections or more attention by the designer are required to control deflections. Strengthwise, no significant ad-vantages result from using Grade 80 bars in tied columns less than 36 in. (91.4 cm square). Less Grade 80 steel is needed for flexura members and I systems but total weight savings are reduced by the longer tension development lengths and lap splice lengths required. From a comparison of estimated in-place costs for Grades 60 and 80 steel, it was shown that small tonnage savings in Grade 80 would actually result in extra costs. Tonnage sav-ings of 10 to 15 percent are required in Grade 80 steel to offset higher material costs.